Envelope-stuffing machines and, more generally, machines for inserting signatures, folded sheets or individual sheets, e.g., letters, into envelopes or between the sides of some other cover, e.g., a folder, generally comprise suction means for drawing apart the opposite sides of the cover to open the mouth thereof and permit the sheets to be inserted.
Reference can be made to German Pat. Nos. 706,317, and 963,125, for example, which provide suction means to open the envelope or some other cover to enable a transport device to introduce the unfolded or folded sheets into the envelope or cover. In the following description, the term "cover" is used generally to refer to an enclosure for paper sheets or the like which can be inserted through a mouth of the unit upon the spreading apart of the opposite sides thereof. Such covers include folders, folded sheets or letter or other envelopes.
In the aforedescribed machines, when the suction force is applied to open the cover or envelope, the transport of the sheets or folded pages to be inserted into the cover or envelope is initiated. These machines suffer, however, from the lack of any control which is intended to ensure transportation or insertion of the sheets into the envelope or cover when the letter is open but which prevents advance of the sheets to the mouth of the envelope or cover when the suction effect is incapable of opening the envelope.
Generally speaking it is the practice to provide mechanical members which are inserted into the opening of the envelope or cover to ensure that the latter is properly opened before the transport of the sheets or sheet to be inserted is commenced. The mechanical member frequently damages the envelope and may even slip so as to miss the opening entirely, thereby interrupting the envelope-stuffing process.